Isn't it time to obsolete interlace formats?

[theAlchemist]

What is the technological reason for using any interlaced video format with HDTV?
As far as I understand the interlacing technique was invented to get around the fluorescent's short persistence phenomenon, in order to reduce flickering on Cathode Ray Tube displays (CRTs). With the invention of the plasma screens and since HDTV targets mostly those screens, this technique seems to be obsolete and not necessary anymore (plasma screens do not suffer from the short persistence like CRTs). I expected any new format to abandon the interlacing technology completely and concentrate on compression using the modern technology (Spatial / Temporal redundancy reduction using Motion Compensation and DCT).
Transmitting 60 fields per second or 30 full frames per second consumes the same bandwidth however if the video is interlaced the receiver must de-interlace it, which consumes serious amount of CPU power and result in inferior quality.
I do give the credit to the expert who decided to make the most advanced HDTV format interlaced. Therefore I assume there must be a reason but I just can't figure it out.
I've asked this in another forum with no convincing answer.
Can you help?
__________________
:thanks:

[mg262]

since HDTV targets mostly [plasma] screensSource for this remark?

also read:
http://www.ics.ele.tue.nl/~dehaan/pdf/73_tronCE_formats.pdf

if the video is interlaced the receiver must de-interlace itIs this true? Why can't it simply display interlaced in the same way that a standard TV does?

[theAlchemist]

I read the paper you suggested. It was written around year 2000 when Plasma and other progressive displays were not available yet and with the objective to improve viewing experience on CRTs using recent technology. (I guess it was Philips's interest to prolong the life of CRTs) Since they discuss only CRTs it is obvious that interlaced format will give the best results.

You ask why progressive displays have to deinterlace and can't just render the interlaced fields one by one skipping the odd and even lines alternately. I guess it is possible to build displays that work that way but the displays available today don't. Also since the persistence of the light emitting material in plasma displays is much shorter then in CRTs the result will appear flickering and inconvenient to watch.

Therefore they all deinterlace before rendering. As far as I understand this is what MS Media Player and Apple Quick Time are doing on PC. I have evidences that Plasma TVs do the same. In many cases you can see that fine horizontal lines such as the line between sealed lips disappear momentarily. This I believe is the result of the deinterlacer.
In my mind there is no doubt that progressive format is the one more suitable for modern displays.
I'm interested to know what the industry thinks about this subject

[Guest]

Interlaced streams have a higher temporal resolution than progressive ones. So, watching high-action sports, for example, is more satisfying (to some people) with an interlaced stream displayed on an interlaced display device. Most display devices sold now, however, are progressive.

[billou2000]

Just to precise few things: progressive TV screens (plasma, lcds) integrate deinterlacing chips that actually deinterlace (wow) interlaced video (25/30hz) but to reconstruct 50/60 progressive frames and not 25, so that the original motion information is not destroyed.

Neuron2 I second you: watching sport at 50 fields per second compared to 25 full frames, is definetely a much more satisfying experience (and for everybody in my opinion). Some TV sport report programs do deinterlace videos to 25 full frames (and generally in a very poor way, like line doubling) to get a more film / dramatic look but it would be a pain to watch live sport that way.

Interlaced is still there in HD (1080i) as it is a good way to get very high resolution and still good motion feeling at 25 fps (50 fields per sec) without doubling the already huge bandwith required for that res/framerate (20 Mbps in MPEG-2 and probably around 10 in AVC).
You'd have to double that rate (40 Mbps in MPEG-2 and 20 Mbps in AVC) to get a smooth motion for sport events at 50 full frame per seconds.
but lower resolution in the HD standard like 1280x720 or 1024x576 can work with 50 full frames per second as the bandwith they require is still acceptable.

[Doom9]

atching sport at 50 fields per second compared to 25 full frames, is definetely a much more satisfying experience (and for everybody in my opinion).Well.. I only watch on progressive sets and unless I'm really drunk, the interlaced lines give me the finger all the time.. in other words, I can spot interlacing pretty reliably. I don't think you'd need 1080i for sports.. get a case of beers, and you can live just fine with 720p @ 50/60 (which is part of the HDTV specs)

I think it's more about TV stations being cheap and not wanting to upgrade their equipment to handle progressive, than anything else.. considering the bitrates being used for SDTV, what the consumer gets to see is of no concern to them whatsoever.

[billou2000]

I think we agree :) Ideally we want 50/60 progressive and having 720p doing just that should be the way to go.
As for the interlacing effects spotted on progressive screens, I think I know what you are talking about but I guess we just have to hope for better deinterlacing algos, that's a tricky problem, look at how many software deinterlacers are available just for avisynth, and none is perfect...

As for current digital SDTV programs I second you : it can be awful and nobody seems to care (worse being sport). It's a bit worrying to think that at some points we are all gonna invest in HD capable equipements and we might still end up with rubbish quality...
But if consumers don't complain, broadcasters have no reason to change that either...
I know too many people who just seem to think that because they have a big plasma tv set and "digital" channels then anything they are watching is awesome even though it's just an awful sea of moving coloured blocks. what can you do:)

[mg262]

look at how many software deinterlacers are available just for avisynth, and none is perfect...None is perfect, but some are very good... but most of them are too CPU intensive for real-time playback/implementation in hardware.

When you have a moment, do try the deinterlacers near the top of this list:

http://forum.doom9.org/showthread.php?p=759778#post759778

I've never had the chance to play with either, but I've been told that a good projector produces much better pictures than large plasma screens.

[Pookie]

For a slower PC (like mine), you can get nice, stutter free full screen playback of 1080i by using VideoLan Player and choosing "discard fields" as the deinterlacer.

[Mug Funky]

I think it's more about TV stations being cheap and not wanting to upgrade their equipment to handle progressive, than anything else.. considering the bitrates being used for SDTV, what the consumer gets to see is of no concern to them whatsoever.

the "consumer" generally would not be able to spot the difference between interlace and progressive without a crash course from a very good teacher. believe me, i've tried to explain it to people who design for TV and it's a disturbingly hard concept to grasp (especially when you get the TFF/BFF confusion, thankyou very much miniDV).

and, speaking from the point of a production company that's too cheap to upgrade, i'd have to say it's a pretty simplistic way of seeing it. TV stations are still catering for analog for the most part. and from a HD perspective, the equipment quite obviously must be upgraded even to support interlace in HDTV. to go to HDTV requires it, period (we all know that).

as far as being cheap, that's understandable. maybe big commercial TV stations have the money, but there are others who do not wish to replace their equipment just yet. try for fun checking out one of these places, and try to put a figure on how much all their equipment cost. and i mean all of it, because it'll all need to be replaced to go to HDTV. where i am now (not a TV station by any means... just a DVD place big enough to handle in a month what TV stations do in half a day) there's about AUD $350,000 worth of gear that would become completely useless if we were to go HD tomorrow. then add to that the cost of new equipment to replace it all (at higher cost of course), and more RAID servers to hold the stuff on... plus re-training all staff in HDTV profiles while upgrading all their machines to something beefy enough to work with it... it'd take several years profit to break even, and right now it's absolutely not worth it, as SDTV is still far more profitable. and that's just for a small DVD house. a smallish TV station would likely have over 3 times the amount of equipment to replace, more staff, and a much much faster throughput.

it's not a case of stinginess on the part of TV stations (though for the huge ones it may well be different), but simply a matter of it not making any kind of sense to ditch the old formats while they're still doing nearly all of the work for the company. until that situation changes, interlace will be something we all have to live with.

now, i agree that interlace in HDTV formats is a stupid idea, but at the very least digital TV must support it in some fashion for SDTV compatibility, so even if we all used 1080p or 720p for everything, a proper HDTV would still need a deinterlacer for SDTV content (which we're awash in - the entire back catalogue of TV for the last 60 or so years... except that which was shot on film and people cared enough for to re-telecine and restore, which is absolutely bugger-all of it).

[Doom9]

the "consumer" generally would not be able to spot the difference between interlace and progressive without a crash course from a very good teacher. believe me,Well.. sit them in front of two not so high quality screens and play the same content.. the deinterlacer will do a bad job for the interlaced stuff and people will ask questions.. they won't know what causes the problem though :(

[theAlchemist]

To sum up this discussion:
1. Most of you agree that progressive content is the best for progressive displays such as plasma TVs.
2. The cost of replacing equipment, compatibility with SD, and unaware consumers are the reasons given for still having interlace formats in HD (I must say none convinced me. After all we are talking about a new format that requires new equipment anyway).
3. Better temporal resolution for sport programs was mentioned as one reason to keep interlace format. We all agree that it is true on non progressive displays I'm still doubtful of the benefit on real progressive displays.

One note for Pookie: When you use discard fields as deinterlacing algorithm you basically reduce resolution by factor of 2. So for 1080i you get 540 (which is equivalent to DS). Doubling the rate and filing in the missing lines (bobbing) is better algorithm. A better yet algorithms require very strong CPU which is not available yet even in the high end commercial equipment.

Thank you for participating.

[Pookie]

Alchemist - Yes, the material looks compromised with Discard. I have an HD playback card which will do 1080i without a hitch, but I just don't like the look as much of the playback.

[-Spud-]

What about 720p vs. 1080i on a progressive scan display unit? Personally I've found no matter what pro-scan display unit I've seen 720p always looks better. Sure the 1080i has a higher res but after deinterlacing I still prefer the 720p way more than 1080i. Colours, contrast, brightness, blacks and greys etc. are all much nicer to look at with a progressive image on a progressive scan display unit.

Is it safe to say aside from resolution progressive scan signals will always look better on a natively progressive scan display unit? I've had many an argument about this with regards to playing Xbox 360 in 720p rather than 1080i on a Plasma. A small handful of ppl claim 1080i looks much better but from what I can see all they are really looking at is the resolution side of things and nothing else.

For example a lets say you had a Plasma capable of a native 1024x1024 resolution. Now because this native resolution is closer to the 1080i signal resolution than a 720p signal the picture would of course be a lot cleaner. But after deinterlacing wouldn't the 720p picture still be superior in evey other way other than resolution?

That other factor with Xbox 360 is that all games are native 720p only and the built-in scaler upscales the internal 720p frame buffer to 1080i meaning your not looking at true 1080i in the first place.